The present invention is related to the following commonly assigned patent applications: Winged Design For Reducing Corner Stray Magnetic Fields, Ser. No. 10/977,315; and Single Notched Shield and Pole Structure With Slanted Wing For Perpendicular Recording, Ser. No. 10/976,479.
The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head traditionally includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic transitions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When a spin valve employs an antiparallel (AP) pinned layer it is referred to as an AP pinned spin valve. An AP spin valve includes first and second magnetic layers separated by a thin non-magnetic coupling layer such as Ru. The thickness of the spacer layer is chosen so as to antiparallel couple the magnetizations of the ferromagnetic layers of the pinned layer. A spin valve is also known as a top or bottom spin valve depending upon whether the pinning layer is at the top (formed after the free layer) or at the bottom (before the free layer).
The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.
Magnetization of the pinned layer is usually fixed by exchange coupling one of the ferromagnetic layers (AP1) with a layer of antiferromagnetic material such as PtMn. While an antiferromagnetic (AFM) material such as PtMn does not in and of itself have a magnetization, when exchange coupled with a magnetic material, it can strongly pin the magnetization of the ferromagnetic layer.
In order to meet the ever increasing demand for improved data rate and data capacity, researchers have recently been focusing their efforts on the development of perpendicular recording systems. A traditional longitudinal recording system, such as one that incorporates the write head described above, stores data as magnetic bits oriented longitudinally along a track in the plane of the surface of the magnetic disk. This longitudinal data bit is recorded by a fringing field that forms between the pair of magnetic poles separated by a write gap.
A perpendicular recording system, by contrast, records data as magnetic transitions oriented perpendicular to the plane of the magnetic disk. The magnetic disk has a magnetically soft underlayer covered by a thin magnetically hard top layer. The perpendicular write head has a write pole with a very small cross section and a return pole having a much larger cross section. A strong, highly concentrated magnetic field emits from the write pole in a direction perpendicular to the magnetic disk surface, magnetizing the magnetically hard top layer. The resulting magnetic flux then travels through the soft underlayer, returning to the return pole where it is sufficiently spread out and weak that it will not erase the signal recorded by the write pole when it passes back through the magnetically hard top layer on its way back to the return pole.
One problem that has arisen as a result of such perpendicular recording systems is that the magnetic medium is particularly susceptible to stray magnetic fields. Relatively large magnetic structures such as the magnetic shields used magnetically isolate the read sensor act as large magnetic antennas. As magnetic antennas, these structures collect and concentrate magnetic fields from a myriad of extraneous, external sources, such as cellular phones, airport security devices and many other such sources.
The magnetically soft underlayer of the medium in a perpendicular magnetic recording system is particularly susceptible to picking up magnetic fields emanating from such magnetic structures. This phenomenon can be understood more clearly with reference to FIG. 1, which shows a magnetic structure 102 which could be for example a magnetic shield or some other structure such as a magnetic pole of a write head. The magnetic structure 102 acts as a magnetic antenna, collecting the extraneous magnetic fields, indicated by field lines 104. This causes a resulting magnetic flux within the magnetic structure, the magnetic flux being represented by flux lines 106. As those skilled in the art will appreciate the lines 104 depict magnetic fields as they travel through space, whereas the lines 106 indicate a resulting magnetic flux traveling through a magnetic medium such as the structure 102. It should be pointed out that, while the flux 106 is being described as resulting from a vertical field, a similar result would occur as from the presence of a field canted at some other angle.
The magnetic flux 102 becomes highly concentrated at the corners of the magnetic structure 102. As a result, a concentrated magnetic field 106 emits from the corners of the magnetic structure 102 traveling to the soft underlayer 108 of the nearby magnetic medium 110. The soft magnetic properties of the magnetically soft underlayer, cause it to strongly attract and absorb magnetic fields. In fact an environmental stray field of just 50 Gauss can result in a field 106 as large as 6000 Gauss being emitted from the magnetic structure 102 While traveling to the soft underlayer 108, this concentrated magnetic field 106 passes through the magnetically hard top layer 112, and in the processes magnetizes the top layer 112. By doing so, the magnetic field 106 completely erases any data that may have been previously recorded on the top layer 112. As can be appreciated, this is very problematic.
Although magnetic structures such as magnetic shields and magnetic poles exhibit the problem described above, such magnetic structures are a necessary part of magnetic recording head and cannot simply be eliminated. Therefore, there is a strong felt need for a design for magnetic structures that can allow efficient performance of the magnetic structure for its intended purpose (such as a magnetic shield) while avoiding such unwanted stray field writing. Such a solution to the above problem would preferably not involve the addition of significant processes complexity and would allow the use of currently available desired magnetic materials.